Neutral Atom Modeling of the Tftr First Wall, Pump Ducts, and Neutral Beams

The DEGAS neutral transport code is used in two separate cases to simulate the neutral beam box and vessel of the Tokamak Fusion Test Reactor (TFTR). For the neutral beam box simulation, known input parameters include the ion density at the source exit and the proportion of input gas that is converted to the high-energy atomic beam. The T° current to the torus is (1.61" ± 0.03) X 10 s~, with the high-energy beam having a median energy above 95 keV. Corresponding results are found for the D° current. In addition, the amount of gas reaching the torus, the pressure, and the flux and energy distributions of the ions and neutrals to the walls are found. For the tritium case, it is calculated that 92.4 ± 0.2% of the input tritium reaches the cryopanels, 6.64 ± 0.05% reaches the torus, and 1.0 ± 0.2% reaches the ion dump. In the second run, DEGAS was used to calculate the neutral atom flux and energy of particles incident on the walls of the vacuum vessel and the neutral pressure in the pump duct of TFTR during a typical supershot with a 50/50 mixture of deuterium-tritium. Output quantities are the current and energy to the bumper limiter and first wall. The total amount of tritium implanted in the vacuum vessel after 150 shots of 1-s duration is estimated to be 0.5 ± 0.1 g in the bumper limiter and 0.042 ± 0.023 g in the outer wall and pumping duct, which is well within the 5-g on-site inventory and the 2-g in-vessel inventory. The implications of these results are discussed.